Vehicle evaporative emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to an engine intake system where the vapors may be inducted into the engine and combusted, thereby improving fuel economy.
In a typical canister purge operation, a canister purge valve (CPV) positioned along a conduit coupling the engine intake system and the fuel canister is opened while the engine is combusting air and fuel. This allows engine intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve (CVV) positioned along a conduit coupling the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, where the desorbed fuel vapors are combusted in the engine, thereby regenerating the adsorbent material for further fuel vapor adsorption.
Diagnostics may be performed on the evaporative emissions control system e.g., to detect undesired evaporative emissions in the system. A common pathway for undesired evaporative emissions in the emissions control system is through the CPV, the result of canister carbon dust accumulation and sealing surface deterioration. As such, diagnostics to detect the presence of undesired evaporative emissions stemming from a CPV may reduce undesired evaporative emissions, and may reduce disturbances to air-fuel ratio that may result from a CPV that is not functioning as desired.
US Patent Application US 20150019066 teaches that in some approaches, pressure readings from a pressure sensor in a fuel tank may be monitored during engine operation while the CPV is commanded closed in order to determine if air and/or fuel vapor may travel through the CPV while closed. For example, if the CPV is closed and the fuel tank is sealed off from atmosphere, a vacuum may build in the fuel tank during engine operation, which is indicative of a pathway for air and/or fuel vapor through the CPV. However, the inventors herein have recognized potential issues with such approaches. Specifically, such a diagnostic may be problematic in modern automobiles such as hybrid electric vehicles (HEVs) and start/stop (S/S), as in such vehicles the engine may be stopped (e.g., no engine rotation) regularly in order to conserve fuel. In another example, some gasoline turbo direct injection (GTDI) engines can spend extensive time in low manifold vacuum modes, wherein a diagnostic for a CPV that relies on engine manifold vacuum may not be possible. Still further, future engines may be vacuum-less, as manifold vacuum is a pumping loss that reduces internal combustion engine efficiency.
The inventors herein have recognized these issues and have developed a method comprising: monitoring a fuel vapor loading state of an adsorbent material positioned in an engine air intake while fuel is being added to a fuel tank that supplies fuel to the engine; and responsive to an indication that an increase in the fuel vapor loading state is greater than a first predetermined threshold: indicating a canister purge valve configured to seal the fuel tank from the engine air intake is degraded.
As one example, the fuel vapor loading state of the adsorbent material is indicated while fuel is being added to the fuel tank based on a monitored temperature change of the adsorbent material, wherein the temperature change is monitored by one or more temperature sensors embedded in the adsorbent material, and wherein a temperature increase indicates the adsorption of fuel vapors from the adsorbent material, and a temperature decrease indicates the desorption of fuel vapors from the adsorbent material.
By monitoring a temperature of an adsorbent material in an engine air intake system, it may be possible to provide the technical result of detecting CPV degradation without having to rotate an engine to produce vacuum. In particular, fuel vapors produced during fuel tank refilling may be captured in an engine air intake adsorbent material if a CPV is degraded. Filling a fuel tank may produce a positive pressure in a fuel tank relative to a pressure in the engine air intake adsorbent material, thereby creating a positive pressure motive force to move fuel vapors from the fuel tank to the engine air intake adsorbent material during conditions where the CPV is degraded. A temperature of the adsorbent material may change in response to adsorption of fuel vapors into the adsorbent material. The adsorbent material temperature change may be indicative of an increase in fuel vapors migrating from the fuel tank to the adsorbent material, and the migration of fuel vapor from the fuel tank to the adsorbent material may be indicative of CPV degradation.
The present disclosure may provide the following advantages. The approach may be beneficial to indicate CPV degradation without having to generate vacuum in the evaporative emissions control system. Additionally, the approach may be implemented without having to add system components so that system performance may be increased without increasing system cost. Further, the approach may reduce the possibility of emitting fuel vapors during conditions of CPV degradation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.